ADF-NALU rebels, a group of Islamist fighters who operate in the eastern border zone, targeted the village of Byalos and killed 23 people with machetes and hatchets

* U.N. peacekeeping mission calls for military action

* Attackers used machetes, hatchets to kill locals

* Second attack attributed to ADF-NALU in 48 hours (Recasts, adds comment from governor, MONUSCO, background on past military campaign against rebels)

By Aaron Ross

KINSHASA, Oct 18 (Reuters) - Suspected Ugandan rebels killed at least 23 people overnight in their second attack near the eastern Congolese town of Beni in 48 hours, the local governor said on Saturday, prompting the U.N. peacekeeping mission to call for renewed military action.

Violence simmers in the eastern Democratic Republic of Congo despite the presence of U.N. peacekeepers and government troops, who last year defeated an insurgency by M23 rebels that posed the most serious threat to Kinshasa's authority since the vast central African country's last war formally ended in 2003.

ADF-NALU rebels, a group of Islamist fighters who operate in the eastern border zone, targeted the village of Byalos and killed 23 people with machetes and hatchets, according to the governor of North Kivu Province Julien Paluku.

"It's the ADF-NALU. The methods they use...these are not deaths from local rebels here, Mai-Mai or groups like that," he told Reuters.

"This is a genocide, the way in which the ADF kills these people," said Omar Kavota, spokesman for the Civil Society of North Kivu, speaking by telephone from Beni, which is about 40 km (25 miles) south of Byalos.

Victims of the attack included one Congolese soldier, said witness Justin Kambale.

Martin Kobler, head of the U.N. peacekeeping mission to Congo said the latest attack was "outrageous" and called for a new military operation against the rebel group.

"I call for decisive joint military actions of FARDC (Congolese army) and MONUSCO (U.N. peacekeeping mission) in order to relieve the population from the terror imposed by the ADF," he said.

There was no immediate comment from a spokesman in North Kivu province for Congo's army on the latest violence.

Maurizio Giuliano, an official at the U.N. Office for the Coordination of Humanitarian Affairs, said thousands of residents had fled the area into the neighbouring Oriental Province. Among them were at least 20 women who said they were raped by the attackers.

SECOND ATTACK

The ADF-NALU operates alongside a string of other local and foreign armed factions in a border region coveted for its mineral wealth. The U.N. mission MONUSCO has estimated that the group has about 500 fighters.

On Wednesday the rebels killed 30 people in an overnight attack on villages near Beni, the U.N.'s mission said on Friday.

Following a ramp-up in rebel attacks, the Congolese government backed by U.N. attack helicopters in January launched an operation against them.

Government spokesman Lambert Mende on Friday maintained that the government had already defeated ADF-NALU.

"Just because there's a terrorist act in Beni doesn't mean that the forces of the army of Congo did not defeat the ADF....Now they have changed tactics. It was a terrorist attack. You don't need an army to commit terrorism."

Christoph Vogel, a researcher on armed groups in Congo, urged caution on attributing blame for the attacks.

"The government and MONUSCO have been very quick in attributing all these attacks to ADF and there is a lack of concrete evidence over whether all of them or some of them are clearly ADF attacks," he said. (Reporting by Aaron Ross; Writing by Matthew Mpoke Bigg and Emma Farge; Editing by Rosalind Russell)